As is known, a gas turbine for aeronautic engines comprises a stator part having a body or outer casing and a rotor part arranged inside and connected to the stator part.
In order to control the deformation that arises due to the effect of the heat load and consequently optimize the clearance between the stator part and the rotor part as the operating temperature changes, it is known to cool the outer casing by directing jets of cold air onto the outer lateral surface of the casing, which usually has a smooth surface. By varying the airflow and directing the air in specific zones, it is possible to control the deformation of the various parts in relative motion.
In currently known solutions, cooling devices are used in which the air is distributed using a tube grid that surrounds the outer casing and comprises a plurality of outer longitudinal air-supply tubes and a plurality of inner circumferential air-distribution tubes. The distribution tubes receive cooling air from the longitudinal tubes and are provided with air outlet openings, which face towards the outer lateral surface and are set apart from each other in a circumferential direction to distribute the air along the entire outer circumferential periphery of the casing.
In order to optimize the impact of the air on the various parts of the casing's outer lateral surface, the above-mentioned outlet openings are sized so as to obtain a desired airflow and the circumferential tubes are placed at a predetermined distance from the outer lateral surface, normally in the order of a few millimeters.
Known cooling devices of the above-defined type, even if universally used, are relatively heavy as the tubes used, in particular those for air distribution, must necessarily be made of steel in order to support the high heat loads due to the close proximity of the circumferential tubes to the outer lateral surface of the casing.
In addition, beyond certain values, the known devices do not allow reducing the airflow for the same level of cooling efficiency or increasing the cooling for the same level of airflow.
Gas turbines equipped with air cooling devices in which the inner circumferential tubes for air distribution are arranged inside outer channels made in the stator part of the turbine are described in patent documents EP 0892 153 A1, US 2005/129499 A1, EP 1 798 382 A2, EP 1 205 637 A1 and EP 2 236 772 A2;